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83 lines
2.8 KiB
Go
83 lines
2.8 KiB
Go
// Copyright 2022 Harness Inc. All rights reserved.
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// Use of this source code is governed by the Polyform Free Trial License
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// that can be found in the LICENSE.md file for this repository.
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package hash
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import (
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"crypto/sha256"
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"fmt"
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"hash"
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)
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// Type defines the different types of hashing that are supported.
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// NOTE: package doesn't take hash.Hash as input to allow external
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// callers to both calculate the hash themselves using this package, or call gitrpc to calculate the hash,
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// without the caller having to know internal details on what hash.Hash implementation is used.
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type Type string
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const (
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// TypeSHA256 represents the sha256 hashing method.
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TypeSHA256 Type = "sha256"
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)
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// AggregationType defines the different types of hash aggregation types available.
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type AggregationType string
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const (
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// AggregationTypeXOR aggregates a list of hashes using XOR.
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// It provides commutative, self-inverse hashing, e.g.:
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// - order of elements doesn't matter
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// - two equal elements having the same hash cancel each other out.
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AggregationTypeXOR AggregationType = "xor"
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)
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// Aggregator is an abstraction of a component that aggregates a list of values into a single hash.
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type Aggregator interface {
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// Empty returns the empty hash of an aggregator. It is returned when hashing an empty Source
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// or hashing a Source who's hash is equal to an empty source. Furthermore, the following is always true:
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// `Hash(s) == Append(Empty(), s)` FOR ALL sources s.
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Empty() []byte
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// Hash returns the hash aggregated over all elements of the provided source.
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Hash(source Source) ([]byte, error)
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// Append returns the hash that results when aggregating the existing hash
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// with the hashes of all elements of the provided source.
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// IMPORTANT: size of existing hash has to be compatible (Empty() can be used for reference).
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Append(hash []byte, source Source) ([]byte, error)
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}
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// New returns a new aggregator for the given aggregation and hashing type.
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func New(t Type, at AggregationType) (Aggregator, error) {
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// get hash factory method to ensure we fail on object creation in case of invalid Type.
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hfm, hashSize, err := getHashFactoryMethod(t)
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if err != nil {
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return nil, err
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}
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switch at {
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case AggregationTypeXOR:
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return &xorAggregator{
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hfm: hfm,
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hashSize: hashSize,
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}, nil
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default:
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return nil, fmt.Errorf("unknown aggregation type '%s'", at)
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}
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}
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// hashFactoryMethod returns a hash.Hash implementation.
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type hashFactoryMethod func() hash.Hash
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// getHashFactoryMethod returns the hash factory method together with the length of its generated hashes.
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// NOTE: the length is needed to ensure hashes of an empty source are similar to hashes of `a <XOR> a`.
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func getHashFactoryMethod(t Type) (hashFactoryMethod, int, error) {
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switch t {
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case TypeSHA256:
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return sha256.New, sha256.Size, nil
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default:
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return nil, -1, fmt.Errorf("unknown hash type '%s'", t)
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}
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}
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